1. Field of the Disclosure
The disclosure relates generally to filtration methods for the purification of proteins. More particularly, the disclosure relates to the low-shear, counter-pressure sterile filtration of proteins susceptible to damage by shear forces (e.g., shear-sensitive proteins, blood coagulation cascade proteins), for example when being transported in a fluid.
2. Brief Description of Related Technology
Purified protein mixtures can be administered to patients for a variety of therapeutic uses. A purified protein mixture prepared for infusion into patients must be sterilized prior to use. A suitable sterilization process for some proteins includes membrane filtration of a purified protein mixture. The filter membrane can be sized to retain (i.e., remove from the protein mixture) particulates, microorganisms, and some viruses, while the proteins are able to pass through the membrane.
However, some proteins are not efficiently recovered as purified, sterilized proteins using conventional methods such as membrane filtration. This effect is most pronounced when attempting to filter proteins that are shear-sensitive and/or part of the blood coagulation cascade. An example of such a protein is the von Willebrand factor (vWF), which circulates in plasma complexed with factor VIII and assists in the regulation of biological blood coagulation activity. Specifically, the vWF proteins are sensitive to shear forces induced by the velocity gradient of a transporting fluid medium, in particular when the vWF proteins pass through or near a filter membrane (i.e., where flow constrictions and circuitous flow paths in the neighborhood of filter membrane pores result in particularly large velocity gradients). Thus, when filtration units are operated at sufficient pressures to ideally generate desirable process flow rates, increased flow rates (and the accompanying increase in induced shear forces) tend to reduce process yield, for example by damaging or destroying the proteins, and/or by reducing the filtration rate over time.
Accordingly, it would be desirable to develop a method of filtering a purified vWF mixture in a manner that does not substantially damage the vWF proteins, yet which method still permits a suitably high process throughput (i.e., filtration rate) over time. Additionally, it would be desirable to develop a filtering method generally applicable to any protein, such that the general protein can be filtered (e.g., sterile filtered) at an efficient rate without incurring substantial damage to/loss of the protein.